Older adults with a balance-related neurological disease or who have experienced previous falling incidents tend to show increase in instability and changes in irregularity of postural control. This study analyzed the impact of differences in balance ability on the instability and irregularity of postural control in older adults without neurological disease and previous fall experiences. The 49 subjects were older adults aged 65 years and above who did not have neurological disease and prior falling incidents during the previous year. The subjects were classified into two groups of 27 healthy (Berg score [Formula: see text]) and 22 balance-impaired older adults (Berg score [Formula: see text]) according to the Berg balance scale. Each subject was asked to hold in the standing position with eyes closed and with eyes open for one minute. Postural sway was measured along with acceleration using an inertial sensor attached to the subject’s waist. The measured postural sway was calculated using linear measures (95% confidence ellipse area, root mean square) that represented instability and nonlinear measures (sample, multi-scale and composite multi-scale entropy) that represented irregularity. All linear measures showed an increase in the average value in the balance-impaired older adult group’ as well as significant differences between the two groups, whereas the nonlinear measures did not show any differences. These findings indicated that differences in instability were not necessarily accompanied by irregularity changes, and the similarities in irregularity were assumed to be the result of the postural control mechanisms of the subjects without neurological diseases and prior fall incidents being similar to those of subjects with physical injuries.